<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>点击</button>
</body>
<script>
    setTimeout(() => {
        console.log("settimeout");
    });
    let cb = function(){
        console.log("cb");
    }
    let ob = new MutationObserver(cb);
    ob.observe(document.body,{
        attributes:true
    })
    // document.querySelector("button").onclick = function(){
        document.body.setAttribute("kkb","value");
    // }


</script>
</html>